Vacuum-assisted suspension for transtibial prostheses was introduced to the field of prosthetics more than 10 years ago. Vacuum systems have been reported to reduce pistoning of the transtibial residual limb within the socket and maintain limb volume.1,2 Eliminating movement or pistoning of the residual limb within the socket contributes to increased comfort and function in persons with a transtibial amputation by reducing peak pressures during ambulation.3 In addition, individuals who wear vacuum- assisted suspension show an improvement in wound healing.4,5 Reasons for improved limb health are not yet fully understood. It is possible that enhanced limb health may be attributed to decreased differences in pressure during stance and swing that is believed to drive fluid out of the residual limb.6
A vacuum system requires the use of a liner, air wick, socket, and outer sealing sleeve. Vacuum is applied between the socket and liner through an air wick, removing air molecules and locking the liner to the socket wall. With the limb firmly locked into the prosthesis, it has been reported that the device feels like it is part of the individual's body. Comments made by individuals who have worn vacuum-assisted suspension systems include: “The vacuum keeps my residual limb solidly and comfortably in place,” and “It feels like I got my leg back.”7
The use of vacuum-assisted suspension technology has yet to be explored in persons with partial foot amputation. Data from the United States, Australia, and the United Kingdom would suggest that partial foot amputation accounts for between 43% and 70% of all amputations8–10 and that generally, partial foot amputations are more common when the cause of amputation is dysvascular.8,10 There are many different devices available to manage persons with partial foot amputation, including diabetic shoes, high top shoes, rocker sole modifications, toe fillers, ankle-foot orthoses, and various prosthetic designs. It has been reported that persons with amputation proximal to the metatarsal heads benefit biomechanically from a device that extends above the ankle to disperse pressure and provide better center of pressure progression.9 It is also important that the individual patient's needs and goals be understood before providing any device.
The motivation for this case study was a patient who had a partial foot amputation because of trauma and an active job that kept him on his feet all day. The patient had problems with callusing and invaginations of the skin of his residuum. Although his current device incorporated the elements that are hypothesized to improve walking (anterior shell, stiff forefoot, and rigid ankle),11 the subject reported difficulty with comfort, security (i.e., the feeling that the device would stay on), limb health, and foot placement while standing and walking. Clinical experience of the authors in the fitting of vacuum-assisted suspension to persons with transtibial amputation led to the idea that better suspension may improve function, comfort, and soft tissue health for this individual. Furthermore, we had observed clinically that use of vacuum-assisted suspension helped to smooth invaginations and diminish callusing in persons with transtibial amputation. Others have observed similar improvements with minor skin problems.3 Therefore, the purpose of this case study was to evaluate the use of a partial foot prosthesis with vacuum-assisted suspension in an active individual with partial foot amputation.
The subject was a 68-year-old man who stood 6 feet tall and weighed 200 pounds. Fifty-six years earlier, the subject suffered a traumatic injury that resulted in a transfemoral amputation on the right side and a partial foot amputation on the left side (Figure 1). The left partial foot amputation was determined to be between a Lisfranc and Chopart level because physical examination revealed a hard, bone-like structure anterior to the calcaneus/talus, but without an x-ray, the presence of remaining tarsal bones could not be confirmed. Problematic issues on the left residual limb included a sensitive bony amputation site (anterior and distal aspects), plantar callusing, neuromas, and invaginations. The subject was an active community ambulator who needed to walk for his job as a deliveryman. He was healthy, independent, willing to take part in his own health care, and had the ability to understand new technology. The subject provided written consent for the release of information about his case.
The most recent device the subject used was a laminated anterior shell socket attached to a prosthetic foot by a pyramid receiver and a four-hole socket attachment plate (Figure 2). The prosthesis had a distal gel pad with a 1/8-inch Plastazote liner glued into the socket. Suspension was achieved with the use of posterior calf and calcaneus straps.
Fabrication of the partial foot prosthesis with vacuum-assisted suspension was performed in several steps. First, an impression was made using plaster bandage of the subject's left residual lower limb that extended proximally to the tibial tubercle. The impression was sent to a liner manufacturer (Evolution Industries, Orlando, FL), and a custom, platinum-cured, silicone liner was fabricated (Figure 3A). The liner was rolled onto the subject's limb, and a second impression was made over the liner using plaster bandage. Next, a positive plaster model was poured. No global or specific modifications were made to the mold, aside from the removal of artifacts and smoothing with a sand screen. The positive mold was then laminated using the lay-up described in Table 1. The lay-up for this lamination was rigid, thick, and strong to ensure that the device would be serviceable for this active subject. After lamination, the socket was trimmed along the medial and lateral midlines to create an anterior shell that allowed the subject to easily step in and don the prosthetic socket.
An Axtion® prosthetic foot (Otto Bock, Minneapolis, MN) was attached to the socket by a pyramid receiver and a four-hole socket attachment plate. The height on the contralateral prosthesis was adjusted to ensure equal limb lengths. The foot shell was trimmed to accommodate a Harmony® e-pulse pump (Otto Bock, Minneapolis, MN). A urethane barb was mounted to the socket and attached to the pump. To hold vacuum, a Harmony® sleeve (Otto Bock, Minneapolis, MN) was pulled over the socket to seal the system. The subject's shoe was donned over the foot shell with the pump inside the shoe. Space was left within the shoe to charge the pump and press the control buttons as needed (Figures 3B–D).
When donning the prosthesis, the subject was instructed to apply Udderly Smooth lotion (Redex Industries, Salem, OH) to the residual limb immediately before donning the silicone liner. This is standard practice with a variety of vacuum-assisted suspension systems. The purpose of a lotion is to eliminate any potential air spaces and reduce friction between the skin and liner. A nylon sheath was then donned over the silicone liner to act as an air wick within the air space from which vacuum was drawn. The subject stepped into the socket and rolled the sealing sleeve proximally until contacting the liner just proximal to the socket edge. Excess liner was then reflected over the sealing sleeve and proximal edge of the socket.
The subject's satisfaction and perceived function with the original prosthesis and the new prosthesis with vacuum-assisted suspension were assessed using a questionnaire constructed by the author (B.A.; Table 2). The questionnaire was administered by the author (B.A.) before initial fitting with the new prosthesis and before any information about the new prosthesis was provided to the subject. The subject was instructed to read and answer all survey questions independently. The questionnaire was readministered after 2 months of using the new prosthesis with vacuum-assisted suspension. This questionnaire did not undergo any rigorous methodological development; rather, questions were selected from the Prosthesis Evaluation Questionnaire12 and modified for use in this case study. The questionnaire consisted of 12 questions answered using an 11-point unipolar scale, where 0 represented that the condition in question did not occur and 10 represented that the condition in question occurred very often.
In addition to the aforementioned questionnaire, eight open-ended questions were administered once after fitting of the new prosthesis to evaluate the subject's opinion of the new prosthesis with vacuum-assisted suspension (Table 3). To document any effects of the new device on residual limb tissue health, photographs of the subject's left residual limb were taken with a digital camera before initial fitting of the new prosthesis, 10 days after initial fitting, and at 2-month follow-up.
The subject's responses to the questionnaire and open-ended questions are provided in Tables 2 and 3, respectively. Photographs of the plantar surface of the subject's left residual limb are shown in Figure 4. Photographs taken at 10 days and 2-month follow-up show that the skin was healthier in overall appearance when compared with the photographs taken at initial fitting. The presence of callusing before initial fitting had broken up and softened at both follow-up visits. The skin in Figures 4B and C appeared more hydrated and vascularized, and the invaginations flattened.
The results of this case study suggest that there may be some benefits to use of a prosthesis with vacuum-assisted suspension in active persons with partial foot amputation. Although this individual was reasonably well satisfied with his function with the previous prosthesis, the new prosthesis with vacuum-assisted technology improved his comfort during standing and walking and decreased pain. A slight disadvantage of the prosthesis with vacuum-assisted suspension identified by our questionnaire was with regards to weight and tiredness while walking long distances. This may be attributed to the thickness, rigidity, and weight of the socket lamination that was used to ensure resilience.
Answers to the open-ended questions suggested that coupling between the residual limb and prosthesis was improved. These comments are consistent with those reported by other users of vacuum-assisted suspension. Fairley7 reported that there are many instances where persons with amputation have commented positively regarding sockets with vacuum-assisted suspension, stating that “It feels like I got my leg back.” Also, our results are similar to those of Brunelli et al.4 who conducted a prospective study that compared pain and walking ability (using the Locomotor Capabilities Index) of two independent groups of subjects with dysvascular transtibial amputation wearing vacuum-assisted suspension or patella tendon bearing sockets. They reported that walking ability and pain were better in the vacuum group.
The photographs of the residual limb suggest improvements in soft tissue health occurred fairly quickly after onset of use of the new prosthesis. Street3 asserted that a nearly universal observation with vacuum-assisted suspension is the reduction or elimination of minor skin problems, whereas Brunelli et al.4 and Traballesi et al.5 documented wound healing with use of vacuum-assisted suspension in persons with transtibial amputation, with ulcers of substantial surface size being fully healed after 4 to 9 months.
People with diabetes are susceptible to skin ulceration because of peripheral neuropathy and vascular insufficiency. Diabetes is the most common pathology leading to partial foot amputation,9 and it has been reported that 28% to 50% of persons with amputation resulting from diabetes have a second amputation within 5 years of their first surgery.13 Diabetic shoes with custom foot orthotics have been widely used over the years to address diabetic foot ulcer issues. Yet, studies have shown that diabetic shoes and custom inserts provide no statistically significant reduction in reulceration rate.14,15 With 82% of lower-limb loss because of dysvascular complications,16 it is crucial that devices decrease interface stresses while minimizing gait deviations. There is obvious need for an alternative device that can decrease the reulceration rate. Given the positive effects of vacuum-assisted suspension on tissue health and healing, it may provide a useful tool for preventing further amputation in persons with diabetes, although this requires more research.
Street3 proposed that there were two main mechanisms for the observed improvement in both minor skin problems and major ulcers when vacuum-assisted suspension was used. First, superior linkage and maintenance of residual limb volume1 reduce peak pressures6 and shear forces experienced by the residual limb. Second, reducing the cyclic positive and negative pressures experienced by the residual limb during walking6 increases blood flow. Compared with pin suspension, vacuum-assisted suspension seems to increase global circulation and fluid exchange and avoid congestion in persons with transtibial amputation.17
Although direct association cannot be made between use of negative pressure in wound therapy and prosthetic suspension because of the difference in mode of application (i.e., vacuum is not applied directly to the skin in prosthetic applications), current thinking regarding the role of tissue deformation in wound healing may help to explain the effects on tissue health that have been anecdotally reported in persons with amputation using vacuum-assisted suspension.3–5,7 It is proposed that vacuum applies mechanical forces to the wound that deform tissues, resulting in deformation of cells, followed by stimulation of growth factor pathways, leading to increased mitosis and production of new tissue.18 It has also been suggested that tensile stresses applied to the skin stimulate cellular proliferation, whereas compressive forces lead to resorption of the underlying tissues.19 Perhaps, it is possible that the skin of the residual limb experiences similar microdeformations when vacuum is used, assuming that the liner is adhered to the skin sufficiently to transfer forces.
It should be noted that the subject in this study did not have diabetes, but he nonetheless experienced skin issues. Because he had a right transfemoral amputation, the left lower limb became the dominant limb and thus subject to greater use. It is possible that this contributed to the poor condition of his residual limb, hastening the development of skin breakdown. The reduction in severity of callusing on the subject's residual limb observed with use of vacuum-assisted suspension may also be attributed to the implementation of a daily moisturizing regimen associated with donning of the liner over the skin of the residual limb. Additional research is required to assess the relative contributions of lotion and vacuum-assisted suspension to soft tissue health.
Even though the prosthesis with vacuum-assisted suspension worked well and the subject was satisfied (i.e., happy), improvements could still be made, including making the prosthesis lighter, less bulky, and more durable. For example, during the 2-month follow-up, the subject broke two filters to the vacuum pump. Increased durability of the sleeve and liner would also improve the quality and resilience of the device.
The use of new technologies in prostheses such as vacuum-assisted suspension can be rewarding but may not be for everyone. With regards to vacuum-assisted suspension, patient selection criteria are similar to that of persons with transtibial amputation: good hygiene, gadget tolerance, good cognition, and compliance are all important factors. The person with amputation must take a more active role in his or her own care, including the willingness to clean and don the liner correctly, monitor the vacuum, make sure the system is sealed, and apply a moisturizing lotion during donning. These are things that the individual must do daily for the system to work properly. In our experience, the individual's agreement to participate in his or her care is one of the main obstacles when it comes to the success of this system. In this particular instance where the subject had bilateral amputations, we adjusted the contralateral limb length to allow for the build height of the Axtion foot. However, use of a lower-profile foot would allow this setup to be used by persons with unilateral amputation without leading to a limb length discrepancy.
This case study was an attempt to document changes in the care of one individual as they transitioned to use of a prosthesis with vacuum-assisted suspension. There are obviously limitations regarding generalizability of the results from one individual to others. Our assessment of the subject's satisfaction and perceived function was accomplished using our own questionnaire. Although this allowed us to tailor questions specifically to our context, the questionnaire has not been validated, and as such, we do not know if it is reliable or repeatable, understandable to the patient, sensitive to what we wanted to measure, or biased. There was also potential for bias inherent in the questionnaire results from the subject perceiving the new device as better simply because it was new and high-tech. An additional limitation is the qualitative evaluation of residual limb soft tissue health using photographs.
Overall, this case study suggests that use of a prosthesis with vacuum-assisted suspension may be a viable design for improving comfort, function, and residual limb health for persons with partial foot amputation. Further research with more subjects using validated measures is required to better understand the potential benefit of vacuum-assisted suspension for persons with partial foot amputation, especially those with diabetes.
This project was conducted in fulfillment of the authors' (BA) orthotic residency requirements and was the recipient of the 2009 Orthotic and Prosthetic Education and Research Foundation (OPERF) Resident Travel Award. Greg Caldwell, CP, and the team at Suburban Orthotics and Prosthetics, Des Plaines, IL for supporting this project and residency.
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KEY INDEXING TERMS: artificial limb; prosthesis; vacuum-assisted suspension; partial foot amputation